Electrochemical upcycling of polyethylene terephthalate: catalyst design, reaction mechanisms, and integrated paired electrolysis

Polyethylene terephthalate (PET) waste has become a persistent global environmental challenge. Electrochemical PET upcycling has recently emerged as a promising strategy. This review provides a comprehensive overview of the reaction pathways, catalyst design principles, and integrated paired-electrolysis strategies for the ethylene glycol oxidation reaction (EGOR). The EGOR proceeds through C₁ (formic acid, FA) and C₂ (glycolic acid, GA) oxidation pathways, with product selectivity governed by several key factors including the catalyst, applied potential and electrolyte conditions. The catalysts for the EGOR focus on noble metals, transition-metal compounds, metal–organic frameworks, organic catalysts, and heterojunction architectures. Besides the anodic EGOR, energy-efficient paired electrolysis systems coupling the EGOR with cathodic reactions, such as hydrogen evolution, two-electron oxygen reduction to H₂O₂, CO₂ reduction, and nitrate reduction, are highlighted for their ability to lower cell voltage and enable the coproduction of value-added chemicals. Mechanistic insights derived from spectroscopy characterization and theoretical calculations are critically examined to elucidate active-site evolution, intermediate stabilization, and reaction-depth control. Finally, key challenges and future opportunities are identified, including selectivity control at industrial current densities, impurity tolerance, product separation, and standardized testing protocols. This review aims to provide a mechanistic and system-level framework to guide the rational design of selective, energy-efficient, and scalable electrochemical PET upcycling technologies.